Hoffman Vapor System Venting

Brenmg

Quick overview

1920 house, had original coal fired boiler which was converted to NG a number of years back.

New boiler was installed in September this year (Utica Boiler 400k BTU) (probably oversized) Pressurtol set to .5

Boiler replacement had been paid for by previous owner of house when we purchased it

Installing contractor is not well versed in steam.

Hoffman differential loop is still intact (Contractor wanted to rip it out)

Initial issues was extreme steam hammer due to improper header piping

Had them install a drop header (Thanks everyone, contractor had no knowledge prior)

Steam trap inserts have been replaced on the majority of the rads (Hoffman No8). Differential temps have been taken, doesnt seem like there are any faulty traps.

Now that we have dry steam we are experiencing what I believe to be "air hammer" at the start of the cycle. EVERY Rad bangs at the beginning. This is what is what I am looking to solve.

I will be adding a vaporstat shortly to run this system down at 4oz. I am assuming this is part of my issue.

Steam main essentially circles the basement and has a Hoffman No 6 vent at the end on the crossover trap line.

Return line has a Hoffman No 10 near the differential loop

I currently have the gas valve throttled down to the boiler as when its is fully firing the distribution lines start banging adding to the chaos.

There is one rad that only begins to heat on the 3rd floor with a air vent on it (not correct) before the cycle ends.

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My question is could the return line venting be causing the banging in the rads at start up.

I also now hear condensate flowing through the return lines in the walls which did not occur before.

I see most recommend Gorton #2 for main venting (replace Hoffman No 6) should I use the same Gorton valve to replace the No 10 or am I just pissing in the wind until the vaporstat is installed

This is potentially a toss up for you vets out there but I appreciate all the help.

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Jamie Hall

That system should be totally silent. Well, maybe the odd expansion noise.

Get rid of the air vent on the radiator. Get rid of the air vent on the steam main — but be certain that the crossover trap there really is working.

I'd replace the main air vent at the boiler with a Gorton #2 — but I'd not do that until a bit later after I'd observed the system.

Now.

First, is the Hoffman Differential Loop still properly piped? The dry returns — all of them — should come together and enter the top, with the main air vent right there or as close to there on the returns as possible. There needs to be a line from the steam header into the side of the Loop, and there needs to be a main return line from the other side of the loop down to the wet returns.

You need a vapourstat for control of the boiler. The cutout should be set at 7 ounces, and the differential (subtractive) at 4 ounces. You also should have a low pressure (0 to 3 psig) gauge to really see what the system is doing; modern vapourstats are not always calibrated correctly.

A critical question. There are likely to be wet returns here and there around the basement, and there may be drips either from the dry returns or the steam mains to those wet returns. Those wet returns must be below the operating water level in the boiler. It sometimes happens with a boiler replacement that the new water line is lower than the old one — and some or all of the returns that are supposed to be wet become dry. That will cause all manner of havoc and must be corrected.

Once you have the pressure under control, does the banging still happen? Under the present pressure setting, if the pressure gets much above 7 ounces the Differential Loop should trip, and with the combination of the vent on the steam main and the one on the radiator I wouldn't be at all surprised if you got some pretty spectacular banging, and so there's not much point in looking for other problems until you get the above items addressed.

If you still have banging, then it's time to check the pipe pitches. All of them.

leaking

400,000 BTU ! Must be a big house in a real cold climate .

Jamie Hall

https://forum.heatinghelp.com/discussion/comment/1833728#Comment_1833728

Cedric's bigger (470,000 BTUh gross)

109A_5

Hello Brenmg,

Was the boiler properly skimmed ?

Brenmg

I have a Vapourstat being delivered tomorrow along with a pressure gauge.

All wet legs run to the floor and back to the hartford loop.

Cant tell for certain if the Hoffman DLoop is correctly piped. Ill take a few pictures and label the piping.

3,900ft2 house in central NY.

Boiler has cleaner in it, no surging of the water level has been observed.

Question 1,

Wouldnt removing the air vent on the supply main cause the uneven heating with the take off on the beginning of the loop to receive steam before the distribution of at the end of main?

My understanding is the goal is to have the entire main hot before steam starts filtering to the rads. Being able to quickly vent the main would allow for that process to be completed quicker. Unless the thought is the main crossover Hoffman No8 trap can handle all the air being pushed through it then vented by the Hoffman 10.

Question 2,

Assuming my boiler is oversized, I am guessing that the boiler will start short cycling once its working at the correct pressure. Other than squeezing the main gas supply valve down, are there any other options to mitigate the shortcycling?

Thank you all for your knowledge. Ill install the Vapourstat tomorrow and let update the group as to what change if any occurs.

Jamie Hall

On question 1. There should be a crossover trap at the end of that main. There was one once — all Hoffman systems had them. If there isn't one now, figure out where it had been and reinstall it. The crossover trap usually was a Hoffman 8, though smaller systems may have had a 7. An 8 is good for 75 to 100 feet of up to 3 inch main.

The operation of the Hoffman Differential Loop is dependent on there being one, and only one, main vent at the loop location. No other vents are permitted anywhere else in the system.

If the boiler is oversize it will cycle with pressure. The on part of the cycle will be shorter with a lower cutoff pressure, this is true. This will burn less fuel for a given length of thermostat call, which is rather a good thing.

You don't mention whether this is a power burner or atmospheric burner. If it's an atmospheric burner, there will be almost no loss in efficiency at all. All you will do is save money. If it is a power burner, it may be possible to downfire it — but that is a job for a person with the knowledge and instruments to be able to do it correctly. Unless the on time is less than 3 or 4 times as long as the off time, though, it's not worth it.

Brenmg

Crossover trap is in place and contains a NO8. The original NO6 vent is before the NO8. Thats why I asked as it has been there over 100 years. I do have a tunstall cage for the NO8 but it seems to be working properly right now.

Boiler is atmospheric so that good.